1. Field of the Invention
The present invention relates to a DC voltage converter having a circuit arrangement for the formation of the actual value of the current and which has an electronic switch arranged in a main power circuit of a DC voltage converter and a current sensor arranged in series with the electronic switch and traversed by ramp-shaped current pulses, whereby the electronic switch has a control input connected to a control output of a control circuit that has an input connected to the output of the circuit arrangement for the formation of the actual value of the current and controls the repetition rate and/or the pulse duty factor of the current pulses output at its control output dependent on the actual value of the current in that the chronologically-rising, momentary value of the ramp-shaped current pulse is compared to a reference value.
2. Description of the Prior Art
A DC voltage converter of the type generally set forth above is disclosed in the German application No. 28 38 009. In this known DC voltage changer a switching transistor is driven by a clock generator with turn-on pulses having a constant operating frequency. In order to regulate the output voltage, the pulse duty factor, i.e. the quotient of the on time of the power switching transistor to the duration of the period, is varied. Given overload at the output of the autoconverter, the current in the power circuit is limited for protecting the components. This is achieved by lowering the output voltage at an admissible output current by shortening the on time. The switching transistor is thereby inhibited as soon as the measured momentary value of the current flowing through the switching transistor exceeds a prescribed limit value.
To this end, the known DC voltage converter contains a current-limiting circuit having a current transformer as a current sensor. This current sensor is followed by an RC filter as a low-pass filter, so that the load voltage is freed of inrush currents. This prevents the inhibiting of the switching transistor from being erroneously and prematurely triggered by the inrush currents.
However, the RC filter can only be optimally dimensioned for a defined current. The utilization of such a low-pass filter therefore leads to a desired result only given comparatively small current ranges.